A conventional smart key system for a vehicle locks and unlocks doors of the vehicle, based on detecting a user with a mobile communicator through wireless communications with the mobile communicator. The system also detects that the mobile communicator is in a passenger compartment of the vehicle and subsequently allows an engine of the vehicle to start on a button push.
The smart key system also controls an operation of unlocking a luggage trunk of the vehicle. Specifically, when the user operates a switch of the mobile communicator to unlock the trunk, the system authenticates the user and unlocks the trunk on a success of the authentication. In addition, when the mobile communicator is locked in the trunk, the system makes an in-trunk communicator communicate with the mobile communicator interactively and gives a warning to the user if it determines that the mobile communicator is in the trunk. In this case, when the user operates a switch on the outer surface of the vehicle for unlocking the trunk, the system unlocks the trunk even if the mobile communicator is in the trunk.
However, the area in which the mobile communicator can communicate with the in-trunk communicator depends on the location of the in-trunk communicator and the shape of the trunk. Therefore, the area is not always within the trunk and sometimes covers places in the passenger compartment. Thus, the in-trunk communicator possibly communicates with the mobile communicator in the passenger compartment.
In such a case, the user may operate a trunk opener lever in the passenger compartment for unlocking and opening the trunk, take out baggage from the trunk with the mobile communicator left in the passenger compartment, and close the trunk. Then, the system possibly determines that the mobile communicator is locked in the trunk and makes the warning although the mobile communicator is in the passenger compartment and not in the trunk. Moreover, the smart key system possibly unlocks the trunk when someone without the mobile communicator operates the switch on the outer surface. This situation in which anyone can open the trunk will cause a security flaw.